Statement I: In humans, the sex of an individual is determined by a pair of autosomes.
Statement II: In the XO type of sex determination, females have two X chromosomes, and males have only one X chromosome.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Only statement II is correct.
Statement I: In humans, the sex of an individual is determined by a pair of autosomes. — False. Humans have 23 pairs of chromosomes. Of these, 22 pairs are autosomes, which are the same in males and females. Sex is decided by the remaining pair, the sex chromosomes (XX in females, XY in males).
Statement II: In the XO type of sex determination, females have two X chromosomes, and males have only one X chromosome. — True. In the XO type, seen in the grasshopper, females have a pair of X chromosomes. Males have only one X besides the autosomes; “O” stands for the missing second sex chromosome.
NCERT Extract:
Sex Determination – “… Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.”
Sex Determination in Humans – “It has already been mentioned that the sex determining mechanism in case of humans is XY type. Out of 23 pairs of chromosomes present, 22 pairs are exactly same in both males and females; these are the autosomes. A pair of X-chromosomes are present in the female, whereas the presence of an X and Y chromosome are determinant of the male characteristic.”